Nice list! If a One should appear in my home at some point (seems quite likely in the next couple of years) this will likely be my first purchase.

But have they removed the "rewind" function?

Nope the rewind function is still there I rarely use it though.  I do use it more often in Forza Horizon because its impossible to win a race if you flip your car which can happen easily in some races.

I never understood why it was there in the first place though, it's kinda like having a resurrect button in a FPS game.

i think gt5 had much less premium cars at release. maybe 200 and gt6 will have more but it is also the second  game on the same console. they didn't start from scratch with all cars... forza 6 will also have more cars as second release on the console. probably the 200 they have now + some of the cars they will release as dlc and some more. and well, like i said, the rest is just a decision if you put more cars in the game just to increase the number or not and turn 10 decided against it. they could obviously also release the game in 2016 and have hundreds more cars or just throw the forza 4 cars in the game. 

i really wanted to get more as well but not if it would mean a later release. i rather get forza 6 when they would release 5 then...

i hate rewind as well in a race but it is good for those who want it. i mean, just take it out in the options and you can't do it in the race. someone said once "if the option is there, i will use it when i make a mistake even if i don't want to" which simply doesn't work if you take this option out in the difficulty settings of the game. you get even more credits then because you get a punishment if you play with this option. like 10% less credits or something like that.

and i think it can be even good. let's say you want to "train" how to drive a corner you have problems with for time trial. instead of restarting the round or driving backwards you simply push the rewind button and drive the corner once more. that is a faster option to do so. 

As long as it's always an option,  isn't used in online rankings and the game design isn't influenced by it, I think it's fine. Just a way of trying to attract ostensibly more casual players to a more difficult type of racing game. 

I don't recall there being more than 50 premium cars added through DLC (paid and free) for GT5 and a lot of them were stock cars. I'll have to look at the DLC packs again.

OT: 2012 Chevrolet Camaro ZL1 - This alone puts Forza's car lineup ahead of GT6 for me though. They could take out 6 of the 72 GTRs in GT6 just to get this one car for all I care. I want one so bad.

Actually I am bit disapointed with the final car list in GT6 also.  At the reveal they said that all the previous cars from GT5 would be in the game but there are a few missing since with the 123 new cars the total number should be 1211 the most noticable absence is the exclusion 2008 Citroen C4 WRC.  Also some of the new cars that where revealt I already used a lot in the Forza games.  But since they also said there would be a lot more DLC cars in the future adding too many cars wouldn't make to much sense most of the DLC will most likely be bought by people that already played GT5 a lot if GT6 is your first GT game it will have more then enough cars to keep you happy for a long time.

Don't have the 2012 Chevy Camero ZL1 in Forza 4 since I don't have any of the DLC except for the free sample cars and the free car packs in that game.  But I do have the car in Forza Horizon and its great in that game it handles and drives better then the 2012 Shelby 1000 when both cars are maxed out at the S class level.